UNPACK_SEQUENCE may occur either in main flow (as in *(a, b) = (1, 2)*)
or as loop iteration variable (*for (a,b) in ..:*)
[fix] reblok:: loop iteration variable is now a reblok instruction (opcode VAR or TUPLE), not just variable name
git-svn-id: http://devedge.bour.cc/svn/reblok/trunk@247 ff29af12-de15-47db-b328-d843b730dfdc